1. Field of the Invention
This invention relates to a rotor for a spindle motor having a rotor magnet on its rotor yoke and an index signal output device.
2. Description of Related Art
For a spindle motor which rotates a rotary recording medium such as a floppy disk, one index signal is required per rotation of the disk in order to determine the starting point for writing data or a similar purpose. This index signal is used to detect the rotation of the floppy disk or the motor during the drive of the floppy disk to generate a ready signal for preparation for writing or reading or for the system to start writing upon formatting and stop it after completion of one rotation.
FIGS. 6 and 8 conceptually show the structure of a spindle motor index position detector which detects the index position for the spindle motor by such an index signal. The structure is composed of a reinforcing plate 101 as a metal mount, a circuit board 102 which is superimposed on the reinforcing plate 101 and a rotor yoke 103 constituting the main body of the rotor. The reinforcing plate 101 consists of a metal plate, and integrally provided at three places around the plate are tabs 101a which are bent uprightly like the letter L. These tabs 101a each have a hole 101b for fixing the reinforcing plate 101 on a floppy disk drive case, etc with screws or other fasteners. In addition, at other four places on the periphery of the reinforcing plate 101 are virtually L-shaped chucking claws 101c which are standing upright. These claws 101c hold the circumference of the circuit board 102 superimposed on the reinforcing plate 101 by pressure from above; application of this pressure is achieved by bending some portion of each of the claws 101c horizontally in a dog-legged manner using a tool, as shown in FIG. 7.
The circuit board 102 consists of an insulating substrate which bears a wiring pattern, components for the spindle motor drive circuit and drive control circuit and so on (not shown in the figures); in the center of the circuit board 102 is a bearing hole 102a in which a bearing 104 with a shaft hole 104a, which is attached to the reinforcing plate 101, is protruding upward. On the outer circumference of this protruding bearing 104 is a core 105 having twelve magnetic poles 105a spaced at regular intervals. A stator coil 106 is wound around each of the magnetic poles 105a. These stator coils 106 constitute three coil sets for three phases U, V and W. These three-phase coil terminals 106a and one common coil terminal 106b are soldered to the right-hand land 102b on the circuit board 102. The core 105 consists of a layered core made by laying a plurality of punched silicon steel plates one on top of another. Also a Hall element 107 for detecting the index position for s rotary recording medium is provided opposite to one of the magnetic poles 105a on the circuit board 102.
As shown in FIGS. 9 and 10, the rotor yoke 103 as the main body of the rotor looks like a shallow bowl turned upside down on the circuit board 102, and has an integral ring flange 103a. Attached to the inner circumference of this flange 103a is a rubber or plastic rotor magnet 108 which forms a ring. The entire circumference of this ring is divided into equal parts as, for example, 16 poles which are magnetized as S and N poles alternately. In some portion of the flange 103a is a window 103b with a specified width in which magnets 108a and 108b as integral parts of the rotor magnet 108 are fitted. These magnets 108a and 108b are protruding outwards from the outer circumference 103a of the flange. Alternatively, the magnets 108a and 108b may be separate from the rotor magnet 108 and the separate magnet 108a may be attached to the outer circumference of the rotor magnet 108.
A shaft 109 is passed through the center hole of the rotor yoke 103; the lower half of the shaft 109 can be inserted into the shaft hole 104a of the bearing 104. This enables the rotor yoke 103 to be rotatably mounted on the circuit board 102, covering the stator coils 106, as shown in FIG. 3. The Hall element 107 is located around and opposite to the outer circumference of the flange 103a. Although not shown in the figures, a thrust bearing is provided at the bottom of the shaft hole 104a and the lower end of the shaft 109 is supported by this thrust bearing. Therefore, the shaft 109 can rotate smoothly while being supported by the shaft hole 104a and the thrust bearing. A chuck or similar device is also fitted on the rotor yoke 103 so that the center hub (not shown) of the floppy disk can rest on it and be held in place by it.
In a spindle motor index position detector as mentioned above, when three-phase alternating current from a three-phase AC power supply is supplied to U-phase, V-phase and W-phase stator coils 106 with phase changes in a predetermined order, a magnetic repulsive force is continuously generated between the rotor magnet 108 on the rotor yoke 103 and the coils, which causes the rotor yoke 103 to rotate on the circuit board 102 as part of the stator. The above mentioned electric current changes are performed by making, for example, three Hall elements as position sensors located between the stator coils 106 detect the rotational position of the rotor yoke 103 and using resulting detection signals as current change control signals.
As the rotor yoke 103 of the spindle motor rotates as described above, the magnets 108a and 108b rotate as well, coming near to or going away from the Hall element 107. When the Hall element 107 is away from the magnets 108a and 108b, it is hardly exposed to a magnetic flux generated by the magnets 108a and 108b and thus the detection output is almost zero. When it comes near to the magnets 108a and 108b, it is exposed to a magnetic flux from the magnets 108a and 108b and the detection output increases or decreases depending on the degree of its distance from them. As a result, the detection output Vf from the Hall element 107 is expressed by the equation Vf=k"PHgr". Consequently, Vf varies in proportion to the amount of magnetic flux inputted to the Hall element 107 as shown in FIG. 11. The detection output is compared with a predetermined reference voltage; a rectangular pulse signal which depends on the result of this comparison is generated and an index signal is generated, for example, at the time of pulse rise of this signal.
The rotor yoke 103 in combination with the rotor magnets 108 constitutes the rotor of the spindle motor; the rotor magnets 108 are attached to the inside of the rotor yoke 103 by gluing, as mentioned above. However, when a glue is applied to the rotor yoke 103 and the rotor magnets 108, it may splash over the surrounding area or overflow the area to be glued. In addition, since it takes a considerable time for the glue to set, it is difficult to decide whether the adhesion is perfect or not, from its external appearance.
This invention solves the above problem. An object of the invention is to ensure that the rotor magnets are securely fixed to the rotor yoke. Another object of it is to provide a spindle motor rotor and an index signal output device that can accurately detect an index signal generated every rotation of the rotor yoke while distinguishing it from other signals and a floppy disk drive which has the rotor and device.
In order to achieve the above objects, according to one aspect of the invention, the spindle motor rotor has: windows at plural places in the flange of the rotor yoke of the spindle motor; projections, integrally provided in some areas of the ring rotor magnet fitted to the inner circumference of the flange, which protrude outwards through the windows, wherein the rotor magnet is joined to the rotor yoke by welding these projections and one of the projections stretches over both an N pole and an S pole of the rotor magnet.
This configuration clearly differentiates magnetic flux changes given by one of the projections stretching over both an N pole and an S pole, from ones given by the other projections, which are intended to fix the rotor magnet to the rotor yoke, so that it is easy to discern the output of an index signal.
According to another aspect of this invention, in the spindle motor rotor, all the projections other than the one stretching over both an N pole and an S pole serve as either an S or N pole.
This makes it possible to accurately discern a zero-crossing signal whose voltage changes in the positive and negative directions continuously or without any interval, from signals whose voltages intermittently change only in the negative or positive direction.
According to another aspect of this invention, the index signal output device for the spindle motor has a magnetic flux detector for detecting a magnetic flux from each of the projections, located opposite to the outer circumference of the flange.
This enables magnetic fluxes from all the projections on the outer circumference of the flange to be converted into discernible electrical signals.
According to another aspect of this invention, the index signal output device for the spindle motor has an index signal output circuit, connected to a magnetic flux detector, which outputs an index signal when the magnetic flux detector detects zero-crossing positive/negative output.
This makes it easy to differentiate zero-crossing output signals which continuously change from positive to negative and vice versa, from the other non-zero-crossing signals, thereby increasing the index signal detection accuracy.
According to another aspect of this invention, a floppy disk drive has the following: windows provided at plural places in a ring flange on a disc rotor yoke of the spindle motor; projections, integrally provided in some areas of a ring rotor magnet fitted to the inner circumference of the flange, which protrude outwards through the above mentioned windows, and a spindle motor rotor in which the rotor magnet is joined to the rotor yoke by welding these projections, and one of the projections stretching over both an N pole and an S pole of the rotor magnet; and a stator which rotatably supports the rotor and has stator coils for giving a repulsive force to the rotor magnet.
This makes it possible to provide a floppy disk drive which clearly differentiates magnetic flux changes given by one projection stretching over both an N pole and an S pole, from ones given by the other projections intended to fix the rotor magnet to the rotor yoke, and thereby easily discerns the output of an index signal.
According to another aspect of the invention, in the floppy disk drive, all the projections other than the one stretching over both an N pole and an S pole of the rotor magnet serve as either S or N poles.
This makes it possible to provide a floppy disk drive which accurately discerns a zero-crossing signal from the above mentioned one projection which continuously changes from positive to negative and vice versa, from signals which intermittently change only in one direction: either negative or positive.
According to another aspect of the invention, the floppy disk drive has the following: windows at plural places in the ring flange on the disc rotor yoke of the spindle motor; projections, integrally provided in some areas of the ring rotor magnet fitted to the inner circumference of the flange, which protrude outwards through the above mentioned windows; the rotor magnet joined to the rotor yoke by welding these projections; and one of the projections stretching over both an N pole and an S pole of the rotor magnet, wherein a magnetic flux detector for detecting magnetic fluxes from each of the projections is located opposite to the outer circumference of the flange.
This makes it possible to provide a floppy disk drive which can be controlled accurately by converting magnetic fluxes from all the projections on the outer circumference of the flange into discernible electrical signals.
According to another aspect of the invention, the floppy disk drive the magnetic flux detector connected with an index signal output circuit which outputs an index signal when the magnetic flux detector detects zero-crossing positive/negative output.
This makes it possible to provide a floppy disk drive which can be accurately controlled by making it easy to differentiate zero-crossing output signals which continuously change from positive to negative and vice versa, from the other non-zero-crossing signals and thereby increasing the index signal detection accuracy.